This invention relates to control circuits and more particularly to circuits which are used in combination with solid state switching devices.
Solid state switching devices which may be variously referred to as solid state power controllers, solid state circuit breakers or solid state switches, offer many performance features which make them preferable to mechanical switching devices in numerous applications. However, each of these switching devices includes a solid state switch which in the open state does not provide a completely open circuit. Leakage current which passes through the switching device while it is in the off state, can result in a shock hazard for maintenance personnel and consequently limits user acceptability of solid state power control devices. Of special concern is a circuit condition that occurs if a load is disconnected as part of a maintenance effort and the solid state power controller output voltage rises to line potential. The use of snubber circuits across the solid state power switch to meet dv/dt requirements increases open power switch leakage current.
It is therefore desirable that solid state power controllers be provided with means for clamping the off state load voltage to a low level to prevent potential shock hazards and eliminate the possibility of inadvertently delivering high voltage to the load terminals of a controller.